Hydroprocessing or hydrotreatment to remove undesirable components from hydrocarbon feed streams is a well known method of catalytically treating such heavy hydrocarbons to increase their commercial value. “Heavy” hydrocarbon liquid streams, and particularly reduced crude oils, petroleum residua, tar sand bitumen, shale oil or liquified coal or reclaimed oil, generally contain product contaminants, such as sulfur, metals and organo-metallic compounds which tend to deactivate catalyst particles during contact by the feed stream and hydrogen under hydroprocessing conditions. Such hydroprocessing conditions are normally in the range of 212° F. to 1200° F. (100 to 650° C.) at pressures of from 20 to 300 atmospheres. Generally such hydroprocessing is in the presence of a catalyst containing group VI or VIII metals such as platinum, molybdenum, tungsten, nickel, cobalt, etc., in combination with various other metallic element particles of alumina, silica, magnesia and so forth having a high surface to volume ratio. More specifically, catalysts utilized for hydrodemetallation, hydrodesulfurization, hydrocracking etc., of heavy oils and the like are generally made up of a carrier or base material; such as alumina, silica, silica-alumina, or possibly, crystalline aluminosilicate, with one more promoter(s) or catalytically active metal(s) (or compound(s)) plus trace materials. Typical catalytically active metals utilized are cobalt, molybdenum, nickel and tungsten; however, other metals or compounds could be selected dependent on the application.
Because these reactions must be carried out by contact of a hydrogen-containing gas with the hydrocarbon feed stream at elevated temperatures and pressures, the major costs of such processing are essentially investment in vessels and associated furnaces, heat exchangers, pumps, piping and valves capable of such service and the replacement cost of catalyst contaminated in such service. Commercial hydroprocessing of relatively low cost feed stocks such as reduced crude oils containing pollutant compounds requires a flow rate on the order of a few thousand up to one hundred thousand barrels per day, with concurrent flow of hydrogen at up to 10,000 standard cubic feet per barrel of the liquid feed. Vessels capable of containing such a reaction process are accordingly cost-intensive both due to the need to contain and withstand corrosion and metal embrittlement by the hydrogen and sulfur compounds, while carrying out the desired reactions, such as demetallation, desulfurization, and cracking at elevated pressure and temperatures. Pumps, piping and valves for handling fluid streams containing hydrogen at such pressures and temperatures are also costly, because at such pressures seals must remain hydrogen impervious over extended service periods of many months.
Further, hydroprocessing catalyst for such a reactor, which typically contains metals such as titanium, cobalt, nickel, tungsten, molybdenum, etc., may involve a catalyst inventory of 500,000 pounds or more at a cost of $2 to $4/lb. Accordingly, for economic feasibility in commercial operations, the process must handle high flow rates and the vessel should be filled with as much catalyst inventory as possible to maximize catalyst activity and run length. Additionally, the down-time for replacement or renewal of catalyst must be as short as possible. Further, the economics of the process will generally depend upon the versatility of the system to handle feed streams of varying amounts of contaminants such as sulfur, nitrogen, metals and/or organic-metallic compounds, such as those found in a wide variety of the more plentiful (and hence cheaper) reduced crude oils, residua, or liquified coal, tar sand bitumen or shale oils, as well as used oils, and the like.
The need for high efficiency in hydroprocessing has led to the development of three basic hydroprocessing reactor configurations and a variety of catalysts for use in them.
These three configurations are as follows: (i) fixed bed downflow reactor systems (ii) ebullated or expanded type upflow reactor systems which are capable of on-stream catalyst replacement and are presently known to industry under the trademarks H-Oi1® and LC Fining®; and (iii) the substantially packed-bed type upflow reactor systems having an on-stream catalyst replacement system, as more particularly described in U.S. Pat. No. 5,076,908 to Stangeland et al., having a common assignee with the current inventions and discoveries.
A fixed bed downflow reactor system may be defined as a reactor system having one or more reaction zones of stationary catalyst, through which feed streams of liquid hydrocarbon and hydrogen flow downwardly and concurrently with respect to each other.
An ebullated or expanded bed reactor system may be defined as a reactor system having an upflow type single reaction zone reactor containing catalyst in random motion in an expanded catalytic bed state, typically expanded from 10% by volume to about 35% or more by volume above a “slumped” catalyst bed condition (e.g. a non-expanded or non-ebullated state).
As particularly described in U.S. Pat. No. 5,076,908 to Stangeland et al., the substantially packed-bed type reactor system is an upflow type reactor system including multiple reaction zones of packed catalyst particles having little or no movement during normal operating conditions of no catalyst addition or withdrawal. In the substantially packed-bed type reactor system of Stangeland et al., when catalyst is withdrawn from the reactor during normal catalyst replacement, the catalyst flows in a downwardly direction under essentially plug flow or in an essentially plug flow fashion, with a minimum of mixing with catalyst in layers which are adjacent either above or below the catalyst layer under observation.
The catalysts of this invention are devised to be particularly advantageous in the upflow reactor systems identified as (ii) and (iii) just above. They could, however, be used in the conventional downflow fixed bed systems if desired.
As discussed in U.S. Pat. No. 5,076,908 to Stangeland et al. and in U.S. Pat. No. 5,472,928 to Scheuerman et al. (also commonly assigned herewith) the size, geometry and physical properties of the particles of a hydroprocessing catalyst can play a major role in determining the catalyst's effectiveness in the upflow “ebullated” bed designs and also in the upflow “packed” bed designs of Stangeland et al. and Scheuerman et al.
The physical characteristics of a catalyst also are important in determining whether or not the catalyst can be continuously renewed or replaced or whether the reactor needs to be periodically shut down to have its catalyst charge replaced. On-stream catalysts replacement or “OCR”, which most commonly involves adding fresh catalyst to the top of a bed and taking spent catalyst out the bottom of the reactor, can offer the advantage of eliminating reactor downtime.
Since the late 1960's, there have been several heavy oil hydroprocessing units built and brought on stream that utilize the ebullated or expanded catalyst bed reactor technology where a hydrocarbon feed stream and hydrogen gas flow upwardly through a dilute phase reaction zone of catalyst in random motion. Stated alternatively, continuous operation of an ebullated or expanded bed hydroprocessing system include the upward flow of a hydrocarbon feed stream and hydrogen gas through a single catalyst containing vessel or a series of catalyst containing vessels. Reactor liquid is recirculated internally at rates sufficient to expand or ebullate the catalyst to produce a dilute phase reaction zone of catalyst in random or ebullating motion.
Catalyst is replaced by continuous or periodic, on-stream removal of catalyst from the vessel followed by addition. As noted above, such ebullation tends to increase the fluid volume in the vessel relative to catalyst volume necessary to hydroprocess the feed stream and hydrogen with the catalyst, with adequate contact time to react the fluids. Further, such ebullated beds tend to result in separation or segregation of “fines” from the larger (and heavier) particles as they pass downwardly through the upflow streams. As frequently happens, and especially where the catalyst is locally agitated, as by eddy currents, the particles tend to abrade by such higher flow rates of the feed streams through the ebullating bed. Depending on the size of the fines, they either travel upward where they contaminate the product or they tend to accumulate in the reactor because they cannot work their way down to the bottom of the bed. Such counterflow systems have also been used because of the relative ease of withdrawing limited amounts of the ebullated catalyst in a portion of the reacting hydrocarbon and hydrogen fluids, particularly where such turbulent flow of the catalyst is needed to assist gravity drainage through a funnel-shaped opening into a central pipe at the bottom of a vessel.
While it has been proposed heretofore to use plug-flow or packed-bed flow of catalyst to reduce such agitation and thus assure uniform disbursement of hydrogen throughout the liquid volume flowing upwardly through the catalyst bed, in general such flow has been controlled by limiting the maximum flow rate that can be tolerated without ebullating or levitating the bed more than about 10%. Further in prior systems where expansion of the bed is limited, hydrogen flow rates are made sufficiently high at the bottom of the bed to assure relative turbulence of the catalyst at the withdrawal point in the vessel. While this does assure such turbulence, it also wastes space, damages the catalyst and permits direct entrainment of hydrogen with catalyst entering the withdrawal tube. Such turbulent flow of catalyst apparently assists gravity removal of catalyst from the vessel.
The basic process designs of the ebullated bed reactors with appropriate mechanical features overcome some of the limitations of the conventional fixed bed reactor. The ebullated or expanded catalyst bed reactor schemes provide ability to replace catalyst on stream and operate with a very “flat” reaction zone temperature profile instead of the steeper pyramiding profile of conventional fixed bed reactors. The nature of the process, with a broad spectrum of catalyst size, shape, particle density, and activity level in random motion in a “dilute phase reaction zone,” creates near isothermal temperature conditions, with only a few degrees temperature rise from the bottom to the top of the reaction zone. Quench fluids are not normally required to limit reaction rates except in cases when series reactors are applied. In other words, the reactor internal recycle oil flow, used to expand (or ebullate) the catalyst bed and maintain distribution (typically 10 to 1 ratio of fresh oil feed) serves also as “internal quench” to control reaction rate and peak operating temperatures. Because the highest temperatures experienced in the reactors are only a few degrees above the average temperature required to maintain processing objectives and not the higher “end of run” peak temperatures experienced in fixed bed reactor systems, the accelerated fouling rate of the catalyst by carbon deposition experienced in conventional fixed bed reactor systems at “end of run” conditions is minimized; however, the normal carbon deposition rate is much greater than that of the fixed bed reactor due to overall operating conditions.
In the U.S. Pat. No. 5,472,928 to Scheuerman et al., there is described a type of catalyst having a particle size, shape and density particularly useful in many upflowing packed bed reactor configurations. This catalyst has proven generally effective in both hydrometallation and hydrodesulfurization reactions. We have now studied that catalyst and made an improvement to it. Representative other patents relating to hydroprocessing of heavy liquid hydrocarbons include:
U.S. Pat. No.5,527,512Bachtel et al.U.S. Pat. No.5,492,617Trimble et al.U.S. Pat. No.5,589,057Trimble et al.U.S. Pat. No.5,498,327Stangeland et al.U.S. Pat. No.5,660,715Trimble et al.U.S. Pat. No.5,648,051Trimble et al.U.S. Pat. No.5,599,440Stangeland et al.U.S. Pat. No.5,885,534Reynolds et al.U.S. Pat. No.5,603,904Bachtel et al.U.S. Pat. No.5,916,529ScheuermanU.S. Pat. No.5,733,440Stangeland et al.U.S. Pat. No.6,086,749Kramer et al. andU.S. Pat. No.6,031,146Bachtel.